Preparation of homopolymers and copolymers of various alpha-amino acids, including phenylalanine, are known as is illustrated, for instance, by the disclosures in U.S. Pat. No. 3,867,520 to Mori et al, U.S. Pat. No. 3,331,814 to Randall et al, U.S. Pat. No. 2,657,972 to Woodward and U.S. Pat. No. 2,729,621 to Miegel. Before the research efforts of the present inventors, however, polymers containing dopa were unknown and could not be produced by the polymerization procedures disclosed in the aforementioned patents. While di- and tripeptides of dopa had been reported in U.S. Pat. No. 3,803,120 to Felix, the higher polymeric forms have not been produced apparently because of the interfering action of the phenolic hydroxyl groups that characterize dopa. Thermal polymerization does not give high molecular weight polymers with a monomer containing such an aromatic hydroxy-containing group.
Dopa and the dopa dimers and trimers have found use medically in the treatment of Parkinsonism. They also have other interesting physiological properties such as that of preventing platelet aggregation. An advantage offered by the dopa-containing polymers of the present invention is that not only do they possess the capability of exhibiting these physiological properties but they do so over extended periods of time because of the polymeric nature of the materials. In the dimer and trimer dopa systems disclosed in the Felix patent, the dopa is believed to become biologically active by cleavage of a di- or tripeptide form. A prolonged effect can be produced from the polymers of the present invention by proteolysis of the polymer to produce either free dopa or oligomers containing dopa, both of which are pharmacologically active. Moreover, the duration of the aforementioned prolonged effect achieved by the dopa-containing polymers of the present invention can be varied by preparing copolymers of the dopa with other amino acids wherein the amount and nature of the amino acid is changed.